Sample selection for secondary synchronization signal (sss) detection

ABSTRACT

Methods and apparatus for selecting samples for secondary synchronization signal (SSS) detection are described. Several alternatives are provided for efficient cell identifier detection. In a first alternative, multiple bursts of a signal received from a cell are sampled with non-uniform spacing between sampling intervals to determine a sequence for cell identification. In a second alternative, samples of a first and a second signal received from a stronger cell are cancelled, and a sequence for detecting a weaker cell is determined by reducing effects of the samples of a third signal received from the weaker cell which do not overlap with the primary synchronization signal (PSS) or SSS of the stronger cell. In a third alternative, a sequence for detecting a weaker cell is determined by reducing effects of any sampled bursts that correspond to a high transmission power portion of a signal from a stronger cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending, commonly assigned,patent application Ser. No. 13/212,812 entitled “SAMPLE SELECTION FORSECONDARY SYNCHRONIZATION SIGNAL (SSS) DETECTION,” filed Aug. 18, 2011,which claims benefit of U.S. Provisional Patent Application Ser. No.61/375,649, filed Aug. 20, 2010 and, the disclosures of which are hereinincorporated by reference in their entirety.

BACKGROUND

I. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more specifically, to selecting samples forsecondary synchronization signal (SSS) detection.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayobserve interference due to transmissions from neighbor base stations.On the uplink, a transmission from the UE may cause interference totransmissions from other UEs communicating with the neighbor basestations. The interference may degrade performance on both the downlinkand uplink.

SUMMARY

Certain aspects of the present disclosure generally relate to selectingsamples for secondary synchronization signal (SSS) detection. Variousaspects are provided for efficient cell identifier detection. In oneaspect, multiple bursts of a signal received from a cell are sampledwith non-uniform spacing between sampling intervals to determine asequence for cell identification. In another aspect, samples of a firstand/or a second signal received from a stronger cell are cancelled, anda sequence for detecting a weaker cell is determined by reducing effectsof the samples of a third signal received from the weaker cell which donot overlap with the first and/or the second signal. In yet anotheraspect, a sequence for detecting a weaker cell is determined by reducingeffects of any sampled bursts that correspond to a high transmissionpower portion of a signal from a stronger cell. The first and/or thesecond signal may comprise a primary synchronization signal (PSS) and/orSSS.

In an aspect of the disclosure, a method for wireless communications isprovided. The method generally includes receiving a first signal fordetermining a cell identity; sampling multiple bursts of the firstsignal during sampling intervals, wherein the bursts are sampled withnon-uniform spacing between the sampling intervals; and determining atleast one sequence of the first signal based on the sampled multiplebursts.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes means for receiving afirst signal for determining a cell identity; means for samplingmultiple bursts of the first signal during sampling intervals, whereinthe bursts are sampled with non-uniform spacing between the samplingintervals, and means for determining at least one sequence of the firstsignal based on the sampled multiple bursts.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes at least one processor anda receiver. The receiver is generally configured to receive a firstsignal for determining a cell identity. The processor is typicallyconfigured to sample multiple bursts of the first signal during samplingintervals, wherein the bursts are sampled with non-uniform spacingbetween the sampling intervals, and to determine at least one sequenceof the first signal based on the sampled multiple bursts.

In an aspect of the disclosure, a computer-program product for wirelesscommunications is provided. The computer-program product generallyincludes a computer-readable medium having code for receiving a firstsignal for determining a cell identity; sampling multiple bursts of thefirst signal during sampling intervals, wherein the bursts are sampledwith non-uniform spacing between the sampling intervals; and determiningat least one sequence of the first signal based on the sampled multiplebursts.

In an aspect of the disclosure, a method for wireless communications.The method generally includes receiving, from a stronger cell, first andsecond signals for determining a cell identity of the stronger cell;receiving, from a weaker cell, a third signal for determining at least aportion of a cell identity of the weaker cell, wherein at least aportion of the third signal overlaps at least one of the first signaland the second signal; sampling the first, second, and third signals;cancelling out samples of at least one of the first and second signals;and determining at least one sequence of the third signal based onsamples of the third signal after reducing effects of samples of anyremaining portion of the third signal that does not overlap the firstsignal and/or the second signal.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes means for receiving, froma stronger cell, first and second signals for determining a cellidentity of the stronger cell; means for receiving, from a weaker cell,a third signal for determining at least a portion of a cell identity ofthe weaker cell, wherein at least a portion of the third signal overlapsat least one of the first signal and the second signal; means forsampling the first, second, and third signals; means for cancelling outsamples of at least one of the first and second signals; and means fordetermining at least one sequence of the third signal based on samplesof the third signal after reducing effects of samples of any remainingportion of the third signal that does not overlap the first signaland/or the second signal.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes at least one processor anda receiver. The receiver is generally configured to receive, from astronger cell, first and second signals for determining a cell identityof the stronger cell, and to receive, from a weaker cell, a third signalfor determining at least a portion of a cell identity of the weakercell, wherein at least a portion of the third signal overlaps at leastone of the first signal and the second signal. The processor istypically configured to sample the first, second, and third signals; tocancel out samples of at least one of the first and second signals; andto determine at least one sequence of the third signal based on samplesof the third signal after reducing effects of samples of any remainingportion of the third signal that does not overlap the first signaland/or the second signal.

In an aspect of the disclosure, a computer-program product for wirelesscommunications is provided. The computer-program product generallyincludes a computer-readable medium having code for receiving, from astronger cell, first and second signals for determining a cell identityof the stronger cell; receiving, from a weaker cell, a third signal fordetermining at least a portion of a cell identity of the weaker cell,wherein at least a portion of the third signal overlaps at least one ofthe first signal and the second signal; sampling the first, second, andthird signals; cancelling out samples of at least one of the first andsecond signals; and determining at least one sequence of the thirdsignal based on samples of the third signal after reducing effects ofsamples of any remaining portion of the third signal that does notoverlap the first signal and/or the second signal.

In an aspect of the disclosure, a method for wireless communications.The method generally includes receiving, from a stronger cell, a firstsignal, wherein first portions of the first signal are transmitted at afirst transmission power and second portions of the first signal aretransmitted at a second transmission power, wherein the secondtransmission power is lower than the first transmission power;receiving, from a weaker cell, a second signal for determining a cellidentity of the weaker cell; sampling multiple bursts of the secondsignal; and determining at least one sequence of the second signal basedon the sampled multiple bursts after reducing effects, to thedetermination, of any sampled multiple bursts corresponding to the firstportions of the first signal.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes means for means forreceiving, from a stronger cell, a first signal, wherein first portionsof the first signal are transmitted at a first transmission power andsecond portions of the first signal are transmitted at a secondtransmission power, wherein the second transmission power is lower thanthe first transmission power; means for receiving, from a weaker cell, asecond signal for determining a cell identity of the weaker cell; meansfor sampling multiple bursts of the second signal; and means fordetermining at least one sequence of the second signal based on thesampled multiple bursts after reducing effects, to the determination, ofany sampled multiple bursts corresponding to the first portions of thefirst signal.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes at least one processor anda receiver. The receiver is generally configured to receive, from astronger cell, a first signal, wherein first portions of the firstsignal are transmitted at a first transmission power and second portionsof the first signal are transmitted at a second transmission power,wherein the second transmission power is lower than the firsttransmission power; and to receive, from a weaker cell, a second signalfor determining a cell identity of the weaker cell. The processor istypically configured to sample multiple bursts of the second signal andto determine at least one sequence of the second signal based on thesampled multiple bursts after reducing effects, to the determination, ofany sampled multiple bursts corresponding to the first portions of thefirst signal.

In an aspect of the disclosure, a computer-program product for wirelesscommunications is provided. The computer-program product generallyincludes a computer-readable medium having code for receiving, from astronger cell, a first signal, wherein first portions of the firstsignal are transmitted at a first transmission power and second portionsof the first signal are transmitted at a second transmission power,wherein the second transmission power is lower than the firsttransmission power; receiving, from a weaker cell, a second signal fordetermining a cell identity of the weaker cell; sampling multiple burstsof the second signal; and determining at least one sequence of thesecond signal based on the sampled multiple bursts after reducingeffects, to the determination, of any sampled multiple burstscorresponding to the first portions of the first signal.

In an aspect of the disclosure, a method for wireless communications.The method generally includes receiving, from a stronger cell, a firstsignal for determining a cell identity of the stronger cell; receiving,from a weaker cell, a second signal for determining a cell identity ofthe weaker cell, wherein the second signal observes interference fromthe first signal; sampling multiple bursts of the first and secondsignals; cancelling out at least a portion of the first signal; anddetermining at least one sequence of the second signal based on sampledbursts of the second signal after reducing effects, to thedetermination, of at least a portion of the sampled bursts of the secondsignal based on the interference from a remaining portion of the firstsignal that is not cancelled.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes means for receiving, froma stronger cell, a first signal for determining a cell identity of thestronger cell; means for receiving, from a weaker cell, a second signalfor determining a cell identity of the weaker cell, wherein the secondsignal observes interference from the first signal; means for samplingmultiple bursts of the first and second signals; means for cancellingout at least a portion of the first signal; and means for determining atleast one sequence of the second signal based on sampled bursts of thesecond signal after reducing effects, to the determination, of at leasta portion of the sampled bursts of the second signal based on theinterference from a remaining portion of the first signal that is notcancelled.

In an aspect of the disclosure, an apparatus for wireless communicationsis provided. The apparatus generally includes at least one processor anda receiver. The receiver is generally configured to receive, from astronger cell, a first signal for determining a cell identity of thestronger cell; and receive, from a weaker cell, a second signal fordetermining a cell identity of the weaker cell, wherein the secondsignal observes interference from the first signal. The processor isgenerally configured to sample multiple bursts of the first and secondsignals; cancel out at least a portion of the first signal; anddetermine at least one sequence of the second signal based on sampledbursts of the second signal after reducing effects, to thedetermination, of at least a portion of the sampled bursts of the secondsignal based on the interference from a remaining portion of the firstsignal that is not cancelled.

In an aspect of the disclosure, a computer-program product for wirelesscommunications is provided. The computer-program product generallyincludes a computer-readable medium having code for receiving, from astronger cell, a first signal for determining a cell identity of thestronger cell; receiving, from a weaker cell, a second signal fordetermining a cell identity of the weaker cell, wherein the secondsignal observes interference from the first signal; sampling multiplebursts of the first and second signals; cancelling out at least aportion of the first signal; and determining at least one sequence ofthe second signal based on sampled bursts of the second signal afterreducing effects, to the determination, of at least a portion of thesampled bursts of the second signal based on the interference from aremaining portion of the first signal that is not cancelled.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless communications network in accordance with certain aspects ofthe present disclosure.

FIG. 2 is a block diagram conceptually illustrating an example of aframe structure in a wireless communications network in accordance withcertain aspects of the present disclosure.

FIG. 2A shows an example format for the uplink in Long Term Evolution(LTE) in accordance with certain aspects of the present disclosure.

FIG. 3 shows a block diagram conceptually illustrating an example of aNode B in communication with a user equipment device (UE) in a wirelesscommunications network in accordance with certain aspects of the presentdisclosure.

FIG. 4 illustrates an example heterogeneous network in accordance withcertain aspects of the present disclosure.

FIG. 5 illustrates example resource partitioning in a heterogeneousnetwork in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates example cooperative partitioning of subframes in aheterogeneous network in accordance with certain aspects of the presentdisclosure.

FIG. 7 illustrates an example primary synchronization signal (PSS)sequence and alternating secondary synchronization signal (SSS)sequences with a periodicity of 5 ms, in accordance with certain aspectsof the present disclosure.

FIG. 8 is a functional block diagram conceptually illustrating exampleblocks executed to determine, from the perspective of the UE, at leastone sequence of a first signal for determining a cell identity based onmultiple bursts sampled with non-uniform spacing between samplingintervals, in accordance with certain aspects of the present disclosure.

FIG. 8A illustrates example components capable of performing theoperations illustrated in FIG. 8.

FIG. 9 illustrates two different overlap scenarios for the signals fordetermining the cell identities of the stronger and the weaker cells, inaccordance with certain aspects of the present disclosure.

FIG. 10 is a functional block diagram conceptually illustrating exampleblocks executed to determine, from the perspective of the UE, at leastone sequence of a signal for determining a cell identity of a weakercell by reducing effects of samples of any portion of the signal thatdoes not overlap signals for determining a cell identity of a strongercell, in accordance with certain aspects of the present disclosure.

FIG. 10A illustrates example components capable of performing theoperations illustrated in FIG. 10.

FIG. 11 is a functional block diagram conceptually illustrating exampleblocks executed to determine, from the perspective of the UE, at leastone sequence of a signal for determining a cell identity of a weakercell by reducing effects of sampled multiple bursts of the second signalcorresponding to portions of a signal received from a stronger cell witha higher transmission power than other portions of the signal receivedfrom the stronger cell with a lower transmission power, from theperspective of the UE, in accordance with certain aspects of the presentdisclosure.

FIG. 11A illustrates example components capable of performing theoperations illustrated in FIG. 11.

FIG. 12 illustrates three different overlap scenarios for time divisionduplexing (TDD) signals for determining the cell identities of astronger cell and weaker cells, in accordance with certain aspects ofthe present disclosure.

FIG. 13 illustrates an overlap scenario for TDD signals for determiningthe cell identities of stronger cells and a weaker cell, in accordancewith certain aspects of the present disclosure.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, certain aspects of the techniquesare described below for LTE, and LTE terminology is used in much of thedescription below.

Example Wireless Network

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork. The wireless network 100 may include a number of evolved NodeBs (eNBs) 110 and other network entities. An eNB may be a station thatcommunicates with user equipment devices (UEs) and may also be referredto as a base station, a Node B, an access point, etc. Each eNB 110 mayprovide communication coverage for a particular geographic area. Theterm “cell” can refer to a coverage area of an eNB and/or an eNBsubsystem serving this coverage area, depending on the context in whichthe term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNBfor a pico cell may be referred to as a pico eNB. An eNB for a femtocell may be referred to as a femto eNB or a home eNB. In the exampleshown in FIG. 1, eNBs 110 a, 110 b, and 110 c may be macro eNBs formacro cells 102 a, 102 b, and 102 c, respectively. eNB 110 x may be apico eNB for a pico cell 102 x. eNBs 110 y and 110 z may be femto eNBsfor femto cells 102 y and 102 z, respectively. An eNB may support one ormultiple (e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNB or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or an eNB). A relay station may also be a UE thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with eNB 110 a and a UE 120 r inorder to facilitate communication between eNB 110 a and UE 120 r. Arelay station may also be referred to as a relay eNB, a relay, etc.

The wireless network 100 may be a heterogeneous network that includeseNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs,relays, etc. These different types of eNBs may have different transmitpower levels, different coverage areas, and different impact oninterference in the wireless network 100. For example, macro eNBs mayhave a high transmit power level (e.g., 20 watts) whereas pico eNBs,femto eNBs, and relays may have a lower transmit power level (e.g., 1watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe timing, and transmissions from different eNBs may not be alignedin time. The techniques described herein may be used for bothsynchronous and asynchronous operation.

A network controller 130 may couple to a set of eNBs and providecoordination and control for these eNBs. The network controller 130 maycommunicate with the eNBs 110 via a backhaul. The eNBs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 may be dispersed throughout the wireless network 100, andeach UE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, etc. A UE maybe a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, atablet, etc. A UE may be able to communicate with macro eNBs, pico eNBs,femto eNBs, relays, etc. In FIG. 1, a solid line with double arrowsindicates desired transmissions between a UE and a serving eNB, which isan eNB designated to serve the UE on the downlink and/or uplink. Adashed line with double arrows indicates interfering transmissionsbetween a UE and an eNB.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth. For example, K may be equal to 128,256, 512, 1024, or 2048 for system bandwidth of 1.25, 2.5, 5, 10, or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz,and there may be 1, 2, 4, 8, or 16 subbands for system bandwidth of1.25, 2.5, 5, 10, or 20 MHz, respectively.

FIG. 2 shows a frame structure used in LTE. The transmission timelinefor the downlink may be partitioned into units of radio frames. Eachradio frame may have a predetermined duration (e.g., 10 milliseconds(ms)) and may be partitioned into 10 subframes with indices of 0 through9. Each subframe may include two slots. Each radio frame may thusinclude 20 slots with indices of 0 through 19. Each slot may include Lsymbol periods, e.g., L=7 symbol periods for a normal cyclic prefix (asshown in FIG. 2) or L=6 symbol periods for an extended cyclic prefix.The 2L symbol periods in each subframe may be assigned indices of 0through 2L−1. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover N subcarriers (e.g.,12 subcarriers) in one slot.

In LTE, an eNB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the eNB. Theprimary and secondary synchronization signals may be sent in symbolperiods 6 and 5, respectively, in each of subframes 0 and 5 of eachradio frame with the normal cyclic prefix (CP), as shown in FIG. 2. Thesynchronization signals may be used by UEs for cell detection andacquisition. The eNB may send a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carrycertain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) inthe first symbol period of each subframe, as shown in FIG. 2. The PCFICHmay convey the number of symbol periods (M) used for control channels,where M may be equal to 1, 2 or 3 and may change from subframe tosubframe. M may also be equal to 4 for a small system bandwidth, e.g.,with less than 10 resource blocks. The eNB may send a Physical HARQIndicator Channel (PHICH) and a Physical Downlink Control Channel(PDCCH) in the first M symbol periods of each subframe (not shown inFIG. 2). The PHICH may carry information to support hybrid automaticrepeat request (HARQ). The PDCCH may carry information on resourceallocation for UEs and control information for downlink channels. TheeNB may send a Physical Downlink Shared Channel (PDSCH) in the remainingsymbol periods of each subframe. The PDSCH may carry data for UEsscheduled for data transmission on the downlink.

The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of thesystem bandwidth used by the eNB. The eNB may send the PCFICH and PHICHacross the entire system bandwidth in each symbol period in which thesechannels are sent. The eNB may send the PDCCH to groups of UEs incertain portions of the system bandwidth. The eNB may send the PDSCH tospecific UEs in specific portions of the system bandwidth. The eNB maysend the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to allUEs, may send the PDCCH in a unicast manner to specific UEs, and mayalso send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element (RE) may cover one subcarrier in one symbol periodand may be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1, and 2. ThePDCCH may occupy 9, 18, 32, or 64 REGs, which may be selected from theavailable REGs, in the first M symbol periods. Only certain combinationsof REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. An eNB may send the PDCCH to the UE in anyof the combinations that the UE will search.

FIG. 2A shows an exemplary format 200A for the uplink in LTE. Theavailable resource blocks for the uplink may be partitioned into a datasection and a control section. The control section may be formed at thetwo edges of the system bandwidth and may have a configurable size. Theresource blocks in the control section may be assigned to UEs fortransmission of control information. The data section may include allresource blocks not included in the control section. The design in FIG.2A results in the data section including contiguous subcarriers, whichmay allow a single UE to be assigned all of the contiguous subcarriersin the data section.

A UE may be assigned resource blocks in the control section to transmitcontrol information to an eNB. The UE may also be assigned resourceblocks in the data section to transmit data to the Node B. The UE maytransmit control information in a Physical Uplink Control Channel(PUCCH) 210 a, 210 b on the assigned resource blocks in the controlsection. The UE may transmit data or both data and control informationin a Physical Uplink Shared Channel (PUSCH) 220 a, 220 b on the assignedresource blocks in the data section. An uplink transmission may spanboth slots of a subframe and may hop across frequency as shown in FIG.2A.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, path loss, signal-to-noiseratio (SNR), etc.

A UE may operate in a dominant interference scenario in which the UE mayobserve high interference from one or more interfering eNBs. A dominantinterference scenario may occur due to restricted association. Forexample, in FIG. 1, UE 120 y may be close to femto eNB 110 y and mayhave high received power for eNB 110 y. However, UE 120 y may not beable to access femto eNB 110 y due to restricted association and maythen connect to macro eNB 110 c with lower received power (as shown inFIG. 1) or to femto eNB 110 z also with lower received power (not shownin FIG. 1). UE 120 y may then observe high interference from femto eNB110 y on the downlink and may also cause high interference to eNB 110 yon the uplink.

A dominant interference scenario may also occur due to range extension,which is a scenario in which a UE connects to an eNB with lower pathloss and lower SNR among all eNBs detected by the UE. For example, inFIG. 1, UE 120 x may detect macro eNB 110 b and pico eNB 110 x and mayhave lower received power for eNB 110 x than eNB 110 b. Nevertheless, itmay be desirable for UE 120 x to connect to pico eNB 110 x if the pathloss for eNB 110 x is lower than the path loss for macro eNB 110 b. Thismay result in less interference to the wireless network for a given datarate for UE 120 x.

In an aspect, communication in a dominant interference scenario may besupported by having different eNBs operate on different frequency bands.A frequency band is a range of frequencies that may be used forcommunication and may be given by (i) a center frequency and a bandwidthor (ii) a lower frequency and an upper frequency. A frequency band mayalso be referred to as a band, a frequency channel, etc. The frequencybands for different eNBs may be selected such that a UE can communicatewith a weaker eNB in a dominant interference scenario while allowing astrong eNB to communicate with its UEs. An eNB may be classified as a“weak” eNB or a “strong” eNB based on the relative received power ofsignals from the eNB received at a UE (and not based on the transmitpower level of the eNB).

FIG. 3 shows a block diagram of a design of a base station or an eNB 110and a UE 120, which may be one of the base stations/eNBs and one of theUEs in FIG. 1. For a restricted association scenario, the eNB 110 may bemacro eNB 110 c in FIG. 1, and UE 120 may be UE 120 y. The eNB 110 mayalso be a base station of some other type. The eNB 110 may be equippedwith T antennas 334 a through 334 t, and the UE 120 may be equipped withR antennas 352 a through 352 r, where in general T≧1 and R≧1.

At the eNB 110, a transmit processor 320 may receive data from a datasource 312 and control information from a controller/processor 340. Thecontrol information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. Thedata may be for the PDSCH, etc. The transmit processor 320 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor320 may also generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 330 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide T output symbolstreams to T modulators (MODs) 332 a through 332 t. Each modulator 332may process a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 332 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. T downlink signals frommodulators 332 a through 332 t may be transmitted via T antennas 334 athrough 334 t, respectively.

At the UE 120, antennas 352 a through 352 r may receive the downlinksignals from the eNB 110 and may provide received signals todemodulators (DEMODs) 354 a through 354 r, respectively. Eachdemodulator 354 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 354 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 356 may obtainreceived symbols from all R demodulators 354 a through 354 r, performMIMO detection on the received symbols, if applicable, and providedetected symbols. A receive processor 358 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 360, and provide decoded control informationto a controller/processor 380.

On the uplink, at the UE 120, a transmit processor 364 may receive andprocess data (e.g., for the PUSCH) from a data source 362 and controlinformation (e.g., for the PUCCH) from the controller/processor 380. Thetransmit processor 364 may also generate reference symbols for areference signal. The symbols from the transmit processor 364 may beprecoded by a TX MIMO processor 366 if applicable, further processed bymodulators 354 a through 354 r (e.g., for SC-FDM, etc.), and transmittedto the eNB 110. At the eNB 110, the uplink signals from the UE 120 maybe received by antennas 334, processed by demodulators 332, detected bya MIMO detector 336 if applicable, and further processed by a receiveprocessor 338 to obtain decoded data and control information sent by theUE 120. The receive processor 338 may provide the decoded data to a datasink 339 and the decoded control information to the controller/processor340.

The controllers/processors 340, 380 may direct the operation at the eNB110 and the UE 120, respectively. The controller/processor 380 and/orother processors and modules at the UE 120 may perform or directoperations for blocks 800 in FIG. 8, operations for blocks 1000 in FIG.10, operations for blocks 1100 in FIG. 11, and/or other processes forthe techniques described herein. The memories 342 and 382 may store dataand program codes for base station 110 and UE 120, respectively. Ascheduler 344 may schedule UEs for data transmission on the downlinkand/or uplink.

Example Resource Partitioning

According to certain aspects of the present disclosure, when a networksupports enhanced inter-cell interference coordination (eICIC), the basestations may negotiate with each other to coordinate resources in orderto reduce or eliminate interference by the interfering cell's giving uppart of its resources. Using eICIC or similar techniques, a UE mayaccess a serving cell using the resources yielded by the interferingcell, where otherwise the UE would experience severe interference.

For example, a femto cell with a closed access mode (i.e., only a memberfemto UE can access the cell) in an open macro cell's coverage cancreate a coverage hole for a macro cell. By making a femto cell give upsome of its resources, the macro UE under the femto cell coverage areacan access the UE's serving macro cell by using the resources yielded bya femto cell.

In a radio access system using OFDM, such as E-UTRAN, the resourcesyielded by the interfering cell may be time-based, frequency-based, or acombination of both. When the yielded resources are time-based, theinterfering cell does not use some of the subframes in the time domain.When the yielded resources are frequency-based, the interfering celldoes not use some of the subcarriers in the frequency domain. When theyielded resources are a combination of both frequency and time, theinterfering cell does not use certain resources defined by frequency andtime.

FIG. 4 illustrates an example scenario where eICIC may allow the macroUE 120 y supporting eICIC (e.g., a Rel-10 macro UE as shown in FIG. 4)to access the macro cell 110 c even when the macro UE 120 y isexperiencing severe interference from the femto cell 110 y, asillustrated by the solid radio link 402. A legacy macro UE 120 u (e.g.,a Rel-8 macro UE as shown in FIG. 4) may not be able to access the macrocell 110 c under severe interference from the femto cell 110 y, asillustrated by the broken radio link 404. A femto UE 120 v (e.g., aRel-8 femto UE as shown in FIG. 4) may access the femto cell 110 ywithout any interference problems from the macro cell 110 c.

According to certain aspects, the resource partitioning between basestations may be done time based. As an example, for E-UTRAN, resourcesmay be partitioned by subframes.

According to certain aspects, networks may support enhanced interferencecoordination, where there may be different sets of partitioninginformation. A first of these may be referred to as semi-static resourcepartitioning information (SRPI). A second of these sets may be referredto as adaptive resource partitioning information (ARPI). As the nameimplies, SRPI typically does not change frequently, and SRPI may be sentto the UE so that the UE can use the resource partitioning informationfor the UE's own operations.

As an example, the resource partitioning may be implemented with 8 msperiodicity (8 subframes) or 40 ms periodicity (40 subframes). Accordingto certain aspects, it may be assumed that frequency division duplexing(FDD) may also be applied such that frequency resources may also bepartitioned. For the downlink (e.g., from an eNB to a UE), thepartitioning pattern may be mapped to a known subframe (e.g., a firstsubframe of each radio frame that has a system frame number (SFN) valuethat is a multiple of an integer N, such as multiples of 4). Such amapping may be applied in order to determine resource partitioninginformation for a specific subframe. As an example, a subframe that issubject to coordinated resource partitioning (e.g., yielded by aninterfering cell) for the downlink may be identified by an index:

-   -   IndexSRPI_DL=(SFN*10+subframe number) mod 8

For the uplink, the SRPI mapping may be shifted, for example, by 4 ms.Thus, an example for the uplink may be:

-   -   IndexSRPI_UL=(SFN*10+subframe number+4) mod 8

SRPI may use the following three values for each entry:

-   -   U (Use): this value indicates the subframe has been cleaned up        from the dominant interference to be used by this cell (i.e.,        the main interfering cells do not use this subframe);    -   N (No Use): this value indicates the subframe shall not be used;        and    -   X (Unknown): this value indicates the subframe is not statically        partitioned. Details of resource usage negotiation between base        stations are not known to the UE.

Another possible set of parameters for SRPI may be the following:

-   -   U (Use): this value indicates the subframe has been cleaned up        from the dominant interference to be used by this cell (i.e.,        the main interfering cells do not use this subframe);    -   N (No Use): this value indicates the subframe shall not be used;    -   X (Unknown): this value indicates the subframe is not statically        partitioned (and details of resource usage negotiation between        base stations are not known to the UE); and    -   C (Common): this value may indicate all cells may use this        subframe without resource partitioning. This subframe may be        subject to interference, so that the base station may choose to        use this subframe only for a UE that is not under severe        interference.

The serving cell's SRPI may be broadcasted over the air. In E-UTRAN, theSRPI of the serving cell may be sent in a master information block(MIB), or one of the system information blocks (SIBs). A predefined SRPImay be defined based on the characteristics of cells, e.g., macro cell,pico cell (with open access), and femto cell (with closed access). Insuch a case, encoding of SRPI in the system overhead message may resultin more efficient broadcasting over the air.

The base station may also broadcast the neighbor cell's SRPI in one ofthe SIBs. For this, SRPI may be sent with its corresponding range ofphysical cell identities (PCIs).

ARPI may represent further resource partitioning information with thedetailed information for the ‘X’ subframes in SRPI. As noted above,detailed information for the ‘X’ subframes is typically only known tothe base stations.

FIGS. 5 and 6 illustrate examples of SRPI assignment as described abovein the scenario with macro and femto cells. A U, N, X, or C subframe isa subframe corresponding to a U, N, X, or C SRPI assignment.

Example Sample Selection for SSS Detection

In LTE, cell identities range from 0 to 503. Synchronization signals aretransmitted in the center 62 resource elements (REs) around the DC toneto help detect cells. The synchronization signals comprise two parts: aprimary synchronization signal (PSS) and a secondary synchronizationsignal (SSS).

FIG. 7 illustrates an example PSS sequence 702 and alternating SSSsequences 704 ₀, 704 ₁ with a periodicity of 5 ms, in accordance withcertain aspects of the present disclosure. The PSS allows a UE to obtainframe timing modulo 5 ms and part of the physical layer cell identifier(cell ID), and specifically cell id modulo 3. Three different PSSsequences exist with each sequence mapping to a disjoint group of 168cell IDs. Based on Zadoff-Chu (ZC) sequences, the PSS sequence is chosenfrom one of 3 sequences based on a PSS Index=Cell ID modulo 3. The samesequence is transmitted every 5 ms as shown in FIG. 7.

The SSS is used by the UE to detect the LTE frame timing modulo 10 msand to obtain the cell ID. The SSS is transmitted twice in each 10 msradio frame as depicted in FIG. 7. The SSS sequences are based onmaximum length sequences, known as M-sequences, and each SSS sequence isconstructed by interleaving, in the frequency-domain, two length-31Binary Phase Shift Keying (BPSK)-modulated sequences. These two codesare two different cyclic shifts of a single length-31 M-sequence. Thecyclic shift indices of the M-sequences are derived from a function ofthe physical layer cell identity group. The two codes are alternatedbetween the first and second SSS transmissions in each radio frame.

In other words, two sequences for a cell ID that alternate every 5 msare transmitted. The SSS sequence is obtained by first choosing from aset of 168 different sequences (different sets for subframes 0 and 5)based on an SSS Index (=floor(Cell ID/3)) and then scrambling the chosensequence using a sequence which is a function of the PSS Index. Hence,while searching for the SSS, if the PSS Index is known, a UE may onlyneed to search up to 168 sequences.

Spacing between the PSS and the SSS helps a UE to distinguish betweenextended cyclic prefix (CP) and normal CP modes and between TDD (timedivision duplex) and FDD (frequency division duplex) modes.

A typical searching operation may involve first locating the PSSsequences transmitted by neighboring eNBs (i.e., determining the timingand the PSS index), followed by SSS detection for the found PSS Indexaround the determined timing.

Both PSS and SSS detection may involve using samples over multiplebursts to improve the chances of detection and reduce false detectionrates. Using multiple bursts provides time diversity. Spacing the burstsfar apart improves the time diversity, but increases the time taken fordetection.

When employing multiple bursts for SSS detection, it is beneficial toinclude the sampled bursts corresponding to both SSS sequences. Forcertain implementations, the bursts used for the multiple-burstdetection are equally spaced. For example, for four bursts:

-   -   5 ms sampling interval spacing involves using the SSS samples        starting at about 0, 5, 10, and 15 ms, which leads to using        subframes alternating between 0 and 5.    -   10 ms sampling interval spacing involves using the SSS samples        starting at about 0, 10, 20, 30 ms, which leads to all subframe        used being either all 0 or all 5.    -   15 ms sampling interval spacing involves using the SSS samples        starting at about 0, 15, 30, 45 ms, which leads to using        subframes alternating between 0 and 5.

Sometimes choosing 5 ms spacing may not be feasible since the time takento perform the SSS detection (i.e., the processing) may be more than 5ms and the UE may not have the next 5 ms samples in the buffer by thetime the UE has completed the detection on the SSS samples in the first5 ms because these next samples may be overwritten with new samples. Inthis case, the minimum spacing between bursts may be 10 ms. The UE mayalso choose a minimum spacing of 10 ms to improve time diversity. Inthis case, if periodic spacing between bursts is used and if both SSSsequences are to be used, the UE is forced to use 15 ms spacing, whichincreases the detection time.

An alternative is to use non-uniform spacing between sampling intervals.For example, for the case of sampling four bursts, the UE could sampleSSS on slots starting at about 0, 10, 25, and 35 ms, which leads tousing subframes 0, 0, 5, and 5, respectively. This leads to a 10 mssaving in detection time over the case of sampling four bursts with 15ms spacing between all the bursts. As another example, for the case ofsampling eight bursts, the UE could sample SSS on slots starting atabout 0, 10, 25, 35, 45, 55, 70, and 80 ms, which leads to usingsubframes 0, 0, 5, 5, 5, 5, 0, and 0, respectively. This leads to a 25ms saving in detection time over the case of sampling eight bursts with15 ms spacing between all the bursts. In this case, the detection timesavings for sampling eight bursts is 25 ms. In another example forsampling eight bursts, the UE could sample SSS on slots starting atabout 0, 10, 20, 30, 45, 55, 65, and 75 ms, which leads to usingsubframes 0, 0, 0, 0, 5, 5, 5, and 5, respectively. In this case, thedetection time savings for sampling eight bursts is 30 ms.

FIG. 8 is a functional block diagram conceptually illustrating exampleblocks 800 executed, from the perspective of the UE, to determine atleast one sequence of a first signal for determining a cell identitybased on multiple bursts sampled with non-uniform spacing betweensampling intervals. Operations illustrated by the blocks 800 may beexecuted, for example, at the processor(s) 358 and/or 380 of the UE 120from FIG. 3.

The operations may begin at block 802 by receiving a first signal fordetermining a cell identity (e.g., an SSS). At block 804, the UE maysample multiple bursts (e.g., 4 bursts) of the first signal duringsampling intervals, wherein the bursts are sampled with non-uniformspacing between the sampling intervals. At least one sequence of thefirst signal may be determined at block 806 based on the sampledmultiple bursts. At block 808, the UE may determine the cell identitybased on the at least one sequence of the first signal. The cellidentity may comprise a physical cell identifier (PCI, or PCID) of aLong Term Evolution (LTE) Release 10 cell.

In an aspect, determining the at least one sequence includes determiningtwo sequences of the first signal, wherein the bursts of the firstsignal alternate between the two sequences. In an aspect, the twosignals are sampled equally.

In certain aspects, in addition to receiving the SSS, a PSS may also bereceived. An additional sequence may be determined based on the PSS andthe cell identity may be determined based on the sequences of the SSSand the PSS.

The operations 800 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 8. For example, operations 800 illustrated in FIG. 8correspond to components 800A illustrated in FIG. 8A. In FIG. 8A, atransceiver (TX/RX) 802A may receive a first signal for determining acell identity. A sampling unit 804A may sample multiple bursts of thefirst signal during sampling intervals, wherein the bursts are sampledwith non-uniform spacing between the sampling intervals. A sequencedetermining unit 806A may determine at least one sequence of the firstsignal based on the sampled multiple bursts. A cell identity determiningunit 808A may determine the cell identity based on the at least onesequence of the first signal.

With the enhanced ICIC (eICIC) solutions in LTE Rel-10 and beyond, thestrong cell(s) may reduce the transmission power as one solution for theUE to acquire the weak cell. In this case, the UE 120 may choose toacquire the weak cell by combining bursts from across those subframeswith less interference from the strong cell.

In synchronous networks as described above with respect to eICIC, thesynchronization signals may overlap with each other. In this casecancelling the synchronization signals of stronger neighboring eNBs andperforming PSS/SSS detection on the cancelled samples may improve thedetection probability of weaker cells. It should be noted that due tothe limited number of PSS sequences, the likelihood of two cells sharingthe same PSS sequence may be high. Therefore, it may be difficult todistinguish PSS Index and, more particularly, the timing of cells thathave the same PSS index. In this case, the UE may perform SSS detectiondirectly for multiple timing hypotheses and multiple PSS indexhypotheses.

As an example, FIG. 9 illustrates two different overlap scenarios forthe signals for determining the cell identities of stronger cells (e.g.,femto cell 102 y) and weaker cells (e.g., macro cell 102 c), inaccordance with certain aspects of the present disclosure. In FIG. 9,two timing hypotheses are considered for the weaker cell: positive andnegative time offset with respect to the strongest cell, due to thepropagation delay from transmission to reception by the UE. In timinghypothesis 1, the SSS 902 of the weak cell overlaps with the PSS 904 andSSS 906 of the strong cell, whose samples may be cancelled by the UE.Consequently, strong interference does not interfere with the samples ofthe SSS 902, and hence, all these samples may be used for weak cell SSSdetection.

For the second hypothesis in FIG. 9, a portion 908 of the samples fromthe SSS 910 of the weaker cell see interference from the stronger cell,whose samples from the other data portion 912 have not been cancelled.In this case, it may be beneficial to ignore (i.e., not consider) thoseportions of the received signal for which cancellation is not done whileperforming SSS detection of the weaker cell. Alternately, the UE mayconsider the samples from portion 908, but may give them lower weightdue to higher noise in that portion 908.

In certain aspects, for timing hypothesis 1, PSS cancellation may beskipped due to additional complexity involved when compared tocancelling SSS only. In such cases, while performing SSS detection forthe weaker cell, those portions of the SSS 902 which overlap with thePSS 904 of the stronger may be ignored.

FIG. 12 illustrates three different overlap scenarios for TDD signalsfor determining the cell identities of stronger cells (e.g., femto cell102 y) and weaker cells (e.g., macro cell 102), in accordance withcertain aspects of the present disclosure. In FIG. 12, three timinghypotheses are considered for the weaker cell. In certain aspects,unlike FDD signals where the PSS and SSS may be allocated on neighboringsymbol periods, PSS/SSS in TDD signals (as shown in FIG. 12) may not beallocated on neighboring symbol periods.

In timing case 1, an SSS 1202 of the weaker cell overlaps with an SSS1204 of the stronger cell. As discussed above, the samples of the SSS1204 may be cancelled. Further, a portion 1206 from the SSS 1202 of theweaker cell may experience interference from the stronger cell whosesamples from the other data portion 1208 have not been cancelled. Inthis case, while performing SSS detection of the weaker cell, theeffects of the portion 1206 of the SSS 1202 of the weaker cellcorresponding to the other data portion 1208 of the stronger cell may bereduced, either by not considering (i.e., ignoring) samples for theportion 1206 or by giving them lower weight.

In timing case 2, an SSS 1210 of the weaker cell overlaps with an SSS1204 of the stronger cell. A portion 1212 from the SSS 1210 of theweaker cell may experience interference from the stronger cell whosesamples from the other data portion 1214 have not been cancelled. Inthis case, while performing SSS detection of the weaker cell, theeffects of the portion 1212 of the SSS 1210 of the weaker cellcorresponding to the other data portion 1214 of the stronger cell may bereduced either by not considering samples for the portion 1212 or bygiving them lower weight.

In timing case 3, an SSS 1216 of the weaker cell overlaps with an SSS1204 of the stronger cell. As discussed above, the samples of the SSS1204 are cancelled. As shown in FIG. 12, the SSS 1204 includes an SSS CPportion 1218. In certain aspects, cancellation of the CP portion 1218may not be very accurate, and thus, a portion 1220 from the SSS 1216 ofthe weaker cell may experience interference from the SSS CP portion 1218(that has not been properly cancelled) in addition to the other dataportion 1214 that has not been cancelled. In this case, while performingSSS detection of the weaker cell, the effects of the portion 1220 of theSSS 1216 of the weaker cell corresponding to the other data portion 1214and the SSS CP portion 1218 of the stronger cell may be reduced, eitherby not considering samples for the portion 1220 or by giving them lowerweight.

Thus, for certain aspects, it may be beneficial to null out at leastpart of the CP portion of a stronger cell (e.g., SSS CP portion 1218)since cancellation of the CP portion may not be accurate.

In certain aspects, when a weaker cell experiences interference frommultiple stronger cells, portions of the weaker cell SSS may have to benulled out that see interference from signals of the multiple cells. Forexample, FIG. 13 illustrates an overlap scenario for TDD signals fordetermining the cell identities of stronger cells and weaker cells, inaccordance with certain aspects of the present disclosure. An SSS 1302of a weaker cell overlaps an SSS 1304 of a stronger cell 1 and an SSS1306 of a stronger cell 2. As discussed above, SSS 1304 and 1306 may becancelled. A portion 1308 from the SSS 1302 may experience interferencefrom the other data portion 1310 of the stronger cell 1 that has notbeen cancelled. In addition, a portion 1312 from the SSS 1302 mayexperience interference from the other data portion 1314 of the strongercell 2 that has not been cancelled. In this case, while performing SSSdetection of the weaker cell, the effects of the portions 1308 and 1312of the SSS 1302 of the weaker cell corresponding to the other dataportions 1310 and 1314, respectively, of the stronger cells may bereduced either by not considering samples for the portions 1310 and1314, or by giving them lower weight. In certain aspects, weights fordifferent portions may be different and may depend on the received powerof the corresponding stronger cells.

FIG. 10 is a functional block diagram conceptually illustrating exampleblocks 1000 executed, from the perspective of the UE, to determine atleast one sequence of a signal for determining a cell identity of aweaker cell by reducing effects of samples of any portion of the signalthat does not overlap signals for determining a cell identity of astronger cell. Operations illustrated by the blocks 1000 may beexecuted, for example, at the processor(s) 358 and/or 380 of the UE 120from FIG. 3.

The operations may begin at block 1002 by receiving, from a strongercell, first and second signals for determining a cell identity of thestronger cell. In an aspect, the first signal includes a PSS from thestronger cell and the second signal includes an SSS from the strongercell. At block 1004, the UE 120 may receive, from a weaker cell, a thirdsignal for determining a cell identity of the weaker cell. In an aspect,the third signal includes an SSS from the weaker cell. At least aportion of the third signal may overlap the first signal and/or thesecond signal. The UE may sample the first, second, and third signals atblock 1006. At block 1008, the UE may cancel out samples of the firstand/or the second signals. At least one sequence of the third signal maybe determined at block 1010 based on samples of the third signal afterreducing effects of samples of any remaining portion of the third signalthat does not overlap the first signal and/or the second signal. Atblock 1012, the UE may determine the cell identity of the weaker cellbased on the at least one sequence of the third signal. For certainaspects, the UE may determine the cell identity of the weaker celldirectly from the at least one sequence of the third signal, withoutfirst determining the PSS, since the SSS is scrambled using the PSSsequence (i.e., by searching over the 168 (sequences for a fixed PSS)*3(all PSS choices)=504 different possibilities for the SSS).

For certain aspects, if there is any remaining portion of the thirdsignal that does not overlap the first signal and/or the second signal,the UE may reduce the effects of the samples of this remaining portionby ignoring (i.e., not considering) the samples of this remainingportion when determining the at least one sequence of the third signal.For other aspects, the UE may weight the samples of the third signal,such that the samples of the remaining portion of the third signal aregiven a lower weight than other samples of the third signal. The UE maythen determine the at least one sequence of the third signal at block1010 based on the weighted samples of the third signal.

In certain aspects, in addition to receiving the SSS from the weakercell, a PSS may also be received from the weaker cell. An additionalsequence may be determined based on the PSS of the weaker cell and thecell identity of the weaker cell may be determined based on thesequences of the SSS and the PSS.

The operations 1000 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 10. For example, operations 1000 illustrated in FIG.10 correspond to components 1000A illustrated in FIG. 10A. In FIG. 10A,a transceiver (TX/RX) 1005A may receive, from a stronger cell (e.g.,eNB₁) at 1002A, first and second signals for determining a cell identityof the stronger cell. At 1004A, the transceiver 1005A may receive, froma weaker cell (e.g., eNB₂), a third signal for determining a cellidentity of the weaker cell, wherein at least a portion of the thirdsignal may overlap the first signal and/or the second signal. A samplingunit 1006A may sample the first, second, and third signals. A cancellingunit 1008A may cancel out samples of the first and/or the secondsignals. A sequence determining unit 1010A may determine at least onesequence of the third signal based on samples of the third signal afterreducing effects of samples of any remaining portion of the third signalthat does not overlap the first signal and/or the second signal. A cellidentity determining unit 1012A may determine the cell identity of theweaker cell based on the at least one sequence of the third signal.

Referring back to FIG. 9, with the enhanced ICIC (eICIC) solutions inRel-10 and beyond, the strong cell(s) may almost blank the other dataportion 1012 (including RS/PBCH/PDSCH and/or control part) when TDM/FDMresource partitioning is used. Alternatively, with the power controlsolution in eICIC, the strong cell(s) may reduce the transmission powerof the other data portion (including RS/PBCH/PDSCH and/or control part).In this case, to detect weaker cells with large timing offsethypothesis, it may be beneficial for the UE to only use (or give higherweight to) the SSS bursts corresponding to the subframes where the otherdata portion is almost blank or is transmitted with reduced transmissionpower.

FIG. 11 is a functional block diagram conceptually illustrating exampleblocks 1100 executed, from the perspective of the UE, to determine atleast one sequence of a signal for determining a cell identity of aweaker cell by reducing effects of sampled multiple bursts of the secondsignal corresponding to portions of a signal received from a strongercell with a higher transmission power than other portions of the signalreceived from the stronger cell with a lower transmission power.Operations illustrated by the blocks 1100 may be executed, for example,at the processor(s) 358 and/or 380 of the UE 120 from FIG. 3.

The operations may begin at block 1102 by receiving, from a strongercell, a first signal, wherein first portions of the first signal aretransmitted at a first transmission power and second portions of thefirst signal are transmitted at a second transmission power, wherein thesecond transmission power is lower (in some cases, much lower) than thefirst transmission power. For certain aspects, the first signal maycomprise at least one of a reference signal (RS), a physical broadcastchannel (PBCH), a physical downlink shared channel (PDSCH), a controlsignal from the stronger cell, or any combination thereof.

At block 1104, the UE 120 may receive, from a weaker cell, a secondsignal for determining a cell identity of the weaker cell and may, atblock 1106, sample multiple bursts of the second signal. In an aspect,the second signal includes an SSS from the weaker cell. At least onesequence of the second signal may be determined at block 1108 based onthe sampled multiple bursts after reducing effects, to thedetermination, of any sampled multiple bursts corresponding to the firstportions of the first signal. At block 1110, the UE may determine thecell identity of the weaker cell based on the at least one sequence ofthe second signal.

For certain aspects, if there are any sampled multiple burstscorresponding to the first portions of the first signal, the UE mayreduce the effects of these sampled multiple bursts by ignoring (i.e.,not considering) these sampled multiple bursts when determining the atleast one sequence of the second signal. For other aspects, the UE mayreduce the effects of these particular sampled multiple bursts byweighting the sampled multiple bursts, such that the sampled multiplebursts corresponding to the first portions of the first signal are givena lower weight than the sampled multiple bursts corresponding to thesecond portions of the first signal. The UE may then determine the atleast one sequence of the second signal at block 1108 based on theweighted sampled bursts of the second signal.

In certain aspects, determining the at least one sequence of the secondsignal includes determining two sequences of the second signal, whereinthe bursts of the second signal alternate between the two sequences.

In certain aspects, in addition to receiving the SSS from the weakercell, a PSS may also be received from the weaker cell. An additionalsequence may be determined based on the PSS, and the cell identity ofthe weaker cell may be determined based on the sequences of the SSS andthe PSS.

The operations 1100 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 11. For example, operations 1100 illustrated in FIG.11 correspond to components 1100A illustrated in FIG. 11A. In FIG. 11A,a transceiver (TX/RX) 1105A may receive, from a stronger cell (e.g.,eNB₁) at 1102A, a first signal, wherein first portions of the firstsignal are transmitted at a first transmission power and second portionsof the first signal are transmitted at a second transmission power,wherein the second transmission power is lower (in some cases, muchlower) than the first transmission power. At 1104A, the transceiver1105A may receive, from a weaker cell (e.g., eNB₂), a second signal fordetermining a cell identity of the weaker cell. A sampling unit 1106Amay sample multiple bursts of the second signal. A sequence determiningunit 1108A may determine at least one sequence of the second signalbased on the sampled multiple bursts after reducing effects, to thedetermination, of any sampled multiple bursts corresponding to the firstportions of the first signal. A cell identity determining unit 1110A maydetermine the cell identity of the weaker cell based on the at least onesequence of the second signal.

Any two or more of the techniques and apparatus described above may becombined for certain aspects. For example, the sampling of the multiplebursts described in FIG. 11 may be performed with non-uniform spacingbetween the sampling intervals, as described in conjunction with FIG. 8.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Forexample, means for transmitting or means for sending may comprise atransmitter, a modulator 354, and/or an antenna 352 of the UE 120depicted in FIG. 3 or a transmitter, a modulator 332, and/or an antenna334 of the eNB 110 shown in FIG. 3. Means for receiving may comprise areceiver, a demodulator 354, and/or an antenna 352 of the UE 120depicted in FIG. 3 or a receiver, a demodulator 332, and/or an antenna334 of the eNB 110 shown in FIG. 3. Means for processing, means fordetermining, means for sampling, and/or means for cancelling out maycomprise a processing system, which may include at least one processor,such as the transmit processor 320, the receive processor 338, or thecontroller/processor 340 of the eNB 110 or the receive processor 358,the transmit processor 364, or the controller/processor 380 of the UE120 illustrated in FIG. 3.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of non-transitory storage medium known in theart. An exemplary storage medium is coupled to the processor such thatthe processor can read information from, and/or write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes bothnon-transitory computer storage media and communication media includingany medium that facilitates transfer of a computer program from oneplace to another. A storage media may be any available media that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, such non-transitory computer-readable mediacan comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store desired program code means in the formof instructions or data structures and that can be accessed by ageneral-purpose or special-purpose computer, or a general-purpose orspecial-purpose processor. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, includes compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk and blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein, but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications, comprising:transmitting, by a base station, a signal, wherein first portions of thesignal are transmitted at a first transmission power and second portionsof the signal are transmitted at a second transmission power, whereinthe second transmission power is lower than the first transmissionpower.
 2. The method of claim 1, wherein the first signal comprises areference signal (RS).
 3. The method of claim 1, wherein the firstsignal comprises a physical broadcast channel (PBCH).
 4. The method ofclaim 1, wherein the first signal comprises a physical downlink sharedchannel (PDSCH).
 5. The method of claim 1, wherein the first signalcomprises a primary synchronization signal (PSS).
 6. The method of claim1, wherein the first signal comprises, a secondary synchronizationsignal (SSS).
 7. The method of claim 1, wherein the first signalcomprises a control signal.
 8. An apparatus for wireless communications,comprising: means for transmitting, by a base station, a signal; meansfor causing first portions of the signal to be transmitted at a firsttransmission power; and means for causing second portions of the signalto be transmitted at a second transmission power, wherein the secondtransmission power is lower than the first transmission power.
 9. Theapparatus of claim 8, wherein the first signal comprises a referencesignal (RS).
 10. The apparatus of claim 8, wherein the first signalcomprises a physical broadcast channel (PBCH).
 11. The apparatus ofclaim 8, wherein the first signal comprises a physical downlink sharedchannel (PDSCH).
 12. The apparatus of claim 8, wherein the first signalcomprises a primary synchronization signal (PSS).
 13. The apparatus ofclaim 8, wherein the first signal comprises, a secondary synchronizationsignal (SSS).
 14. The apparatus of claim 8, wherein the first signalcomprises a control signal.
 15. An apparatus for wirelesscommunications, comprising: a transmitter configured to transmit asignal; and at least one processor configured to: transmit, by a basestation, the signal, wherein first portions of the signal aretransmitted at a first transmission power and second portions of thesignal are transmitted at a second transmission power, wherein thesecond transmission power is lower than the first transmission power.16. The apparatus of claim 15, wherein the first signal comprises areference signal (RS).
 17. The apparatus of claim 15, wherein the firstsignal comprises a physical broadcast channel (PBCH).
 18. The apparatusof claim 15, wherein the first signal comprises a physical downlinkshared channel (PDSCH).
 19. The apparatus of claim 15, wherein the firstsignal comprises a primary synchronization signal (PSS).
 20. Theapparatus of claim 15, wherein the first signal comprises, a secondarysynchronization signal (SSS).
 21. The apparatus of claim 15, wherein thefirst signal comprises a control signal.
 22. A computer-program productfor wireless communications, stored on a non-transitorycomputer-readable medium, and comprising code for performing the stepsof: transmitting, by a base station, a signal; causing first portions ofthe signal to be transmitted at a first transmission power; and causingsecond portions of the signal to be transmitted at a second transmissionpower, wherein the second transmission power is lower than the firsttransmission power.
 22. The computer-program product of claim 1, whereinthe first signal comprises a reference signal (RS).
 23. Thecomputer-program product of claim 1, wherein the first signal comprisesa physical broadcast channel (PBCH).
 24. The computer-program product ofclaim 1, wherein the first signal comprises a physical downlink sharedchannel (PDSCH).
 25. The computer-program product of claim 1, whereinthe first signal comprises a primary synchronization signal (PSS). 26.The computer-program product of claim 1, wherein the first signalcomprises, a secondary synchronization signal (SSS).
 27. Thecomputer-program product of claim 1, wherein the first signal comprisesa control signal.